Class identification (ParkingLot, Floor, Spot, Vehicle) in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the role of the ParkingLot class in a parking system?

The ParkingLot class manages the entire parking area. It keeps track of floors, available spots, and overall capacity.

beginner

What does the Floor class represent in a parking system?

The Floor class represents a single level within the ParkingLot. It contains multiple parking spots and manages their availability.

beginner

What is the purpose of the Spot class in the parking system?

The Spot class represents an individual parking space. It can be assigned to a Vehicle and tracks if it is occupied or free.

beginner

How does the Vehicle class fit into the parking system design?

The Vehicle class represents a car or other vehicle that needs parking. It holds details like vehicle type and license number.

intermediate

Why is it important to identify classes like ParkingLot, Floor, Spot, and Vehicle separately?

Separating these classes helps organize the system clearly. Each class has a focused responsibility, making the design easier to manage and scale.

Which class is responsible for managing multiple floors in a parking system?

A ParkingLot

B Floor

C Spot

D Vehicle

The ParkingLot class manages multiple floors, overseeing the entire parking structure.

What does a Spot class instance represent?

A A parking space

B The entire parking lot

C A floor in the parking lot

D A vehicle parked

Spot represents an individual parking space where vehicles can park.

Which class would store a vehicle's license number?

A ParkingLot

B Floor

C Spot

D Vehicle

Vehicle class holds details about the vehicle, including license number.

If you want to check if a parking spot is free, which class should you query?

A ParkingLot

B Floor

C Spot

D Vehicle

Spot class tracks whether it is occupied or free.

Which class acts as a container for multiple Spot objects?

A Vehicle

B Floor

C ParkingLot

D Spot

Floor contains multiple Spot instances representing parking spaces on that level.

Describe the responsibilities of the ParkingLot, Floor, Spot, and Vehicle classes in a parking system.

Think about how a real parking garage is organized from big to small parts.

Explain why separating the parking system into these classes helps in system design.

Consider how dividing tasks among team members makes work easier.

Practice

1. Which class in a parking system is responsible for managing multiple floors?

easy

A. ParkingLot

B. Floor

C. Spot

D. Vehicle

Solution

1. Step 1: Understand the role of ParkingLot

   The ParkingLot class represents the entire parking area and manages multiple floors within it.

2. Step 2: Compare with other classes

   Floor manages spots on a single level, Spot represents a single parking space, and Vehicle represents the car or bike.

3. Final Answer:

   ParkingLot -> Option A

4. Quick Check:

   ParkingLot manages floors = C [OK]

Hint: ParkingLot holds floors; floors hold spots [OK]

Common Mistakes:

• Confusing Floor as managing multiple floors
• Thinking Spot manages floors
• Assigning Vehicle to manage floors

2. Which of the following is the correct way to represent a parking spot in a class diagram?

easy

A. class Vehicle { int spotNumber; boolean isOccupied; }

B. class Spot { int spotNumber; boolean isOccupied; }

C. class Floor { int spotNumber; boolean isOccupied; }

D. class ParkingLot { int spotNumber; boolean isOccupied; }

Solution

1. Step 1: Identify the class representing a parking spot

   The Spot class should have attributes like spotNumber and isOccupied to represent a parking space.

2. Step 2: Check other classes for correctness

   Vehicle represents cars, Floor represents a level, and ParkingLot represents the whole area, so they should not have spotNumber or isOccupied attributes.

3. Final Answer:

   class Spot { int spotNumber; boolean isOccupied; } -> Option B

4. Quick Check:

   Spot class holds spot info = A [OK]

Hint: Spot class holds spot details like number and occupancy [OK]

Common Mistakes:

• Assigning spot attributes to Vehicle
• Putting spotNumber in Floor or ParkingLot
• Confusing class roles in diagram

3. Given the following code snippet, what will be the output?

class Vehicle {
  String licensePlate;
  Vehicle(String plate) { licensePlate = plate; }
}
class Spot {
  Vehicle parkedVehicle;
  boolean isOccupied() { return parkedVehicle != null; }
}
Spot spot = new Spot();
System.out.println(spot.isOccupied());

medium

A. true

B. Compilation error

C. null

D. false

Solution

1. Step 1: Analyze Spot initialization

   The Spot object is created but parkedVehicle is not assigned, so it defaults to null.

2. Step 2: Evaluate isOccupied method

   isOccupied returns true if parkedVehicle is not null; here it is null, so it returns false.

3. Final Answer:

   false -> Option D

4. Quick Check:

   parkedVehicle is null, so isOccupied() = false [OK]

Hint: Unassigned vehicle means spot is free (false) [OK]

Common Mistakes:

• Assuming default boolean is true
• Confusing null with false
• Expecting compilation error due to missing constructor

4. Identify the error in this class design snippet:

class Floor {
  List<Spot> spots;
  void addSpot(Spot s) {
    spots.add(s);
  }
}

medium

A. Spot class should be inside Floor class

B. Method addSpot should return boolean

C. spots list is not initialized before adding

D. Floor class should not have spots list

Solution

1. Step 1: Check initialization of spots list

   The spots list is declared but not initialized, so calling add on it will cause a runtime error.

2. Step 2: Validate other options

   Returning boolean is optional, Spot class can be separate, and Floor should have spots list to manage spots.

3. Final Answer:

   spots list is not initialized before adding -> Option C

4. Quick Check:

   Uninitialized list causes error = A [OK]

Hint: Always initialize lists before use [OK]

Common Mistakes:

• Ignoring list initialization
• Thinking method return type matters here
• Believing Spot must be nested class

5. You want to design a system where each Vehicle can only park in a Spot that matches its size (e.g., small, medium, large). Which class design change best supports this requirement?

hard

A. Add a size attribute to both Vehicle and Spot classes and check compatibility before parking

B. Add a size attribute only to Vehicle class and ignore Spot size

C. Add a size attribute only to Spot class and ignore Vehicle size

D. Remove size attributes and allow any Vehicle to park anywhere

Solution

1. Step 1: Understand size matching requirement

   Both Vehicle and Spot need size attributes to compare and ensure compatibility.

2. Step 2: Evaluate options

   Ignoring size in either class prevents proper matching; removing size ignores requirement.

3. Final Answer:

   Add a size attribute to both Vehicle and Spot classes and check compatibility before parking -> Option A

4. Quick Check:

   Size match needs attributes in both classes = B [OK]

Hint: Both Vehicle and Spot need size info to match [OK]

Common Mistakes:

• Adding size to only one class
• Ignoring size and allowing any parking
• Confusing attribute placement